Bowden cable coupler

This is a Bowden cable coupler. It joins Bowden cables. Filament passes easily from one cable to another. With an M4 nut, the grip on a standard sized (4mm OD) bowden cable is strong enough not to detach during prints. One side lets you slip a Bowden cable in and out to allow for easy detachment.

##Why?
* Easy to detach
* Corrects mistakes made from undersizing Bowden cables
* Allows coupling tubes of different material, e.g. teflon with PEEK.

I started making this design afte